Reduction Of Power Consumption

ABSTRACT

The invention relates to a method for temporary reduction of electrical power consumption for cooling of buildings where the cooling energy is stored in slab or wall, comprising the step of storing cooling energy in at least some part of the slab ( 4 ) or the wall ( 1,2,3 ) by means of that, during at least one period of time when the electrical transmission network system can supply the necessary electrical cooling machine power, supply cooling machine cooled supply air to channels ( 5 ) arranged in the slab ( 4 ) or the wall ( 1,2,3 ), and the step that, during at least one period of time when the electrical transmission network system is highly loaded, reduce the electrical power consumption of the cooling machine ( 28 ) and at the same time convey supply air through the building through the mentioned channels ( 5 ), which supply air when entering the channel ( 5 ) is warmer than the surrounding slab surface or wall surface adjacent to supply air terminal devices ( 6 ), hereby using the earlier in the slab ( 4 ) or wall ( 1,2,3 ) stored cooling energy to cool the supply air.

FIELD OF THE INVENTION

The present invention relates to a method for temporary reduction ofpower consumption for cooling of buildings.

BACKGROUND

During recent years an increased use of electricity has resulted in thatthe production capacity and the electrical transmission network systemshave been over-used. This concerns above all over-developed city centreswith large shares of offices as these buildings must be provided withnecessary power for lighting, computers with peripheral equipment andabove all for cooling equipment. The last mentioned is of course evenmore of interest in hotter climates, for example near the equator.

The reason for over-use of electrical transmission network systems isthe lack of accessible power for cooling machines when the offices openin the morning and all of the cooling equipment is turned on almostsimultaneously. During the rest of the day the power is then furtherincreased when the outdoor temperature increases and the supply air forventilation of the offices needs more cooling. To be able to manage thesupply during the most critical period, very radical measures maysometimes be demanded. The department of energy in a country may forexample demand that the power consumption of a building is reduced by50% during 5 hours. To increase the cost for the power which is consumedduring a certain time of the day may also be a way to decrease the powerconsumption.

A method which has been developed to manage the lack of electrical powerfor the cooling machines is district cooling, where one in cities nearoceans or big lakes can obtain direct cooling, provided that the waterin the ocean or the lake is cold enough, by burying in the streets largeinsulated conduits providing the buildings with necessary cooling waterpower through heat exchangers, hereby decreasing the power consumed bythe cooling machines. Air treatment and cooling plants that are used inthis cooling method are mainly in operation only during the officehours. In which way the marine local environment will be affected in thelong term is still unclear. The drawbacks with district cooling areseveral. The investment cost is high and the buildings must be situatedclose enough together and near a water system in order for it to bepractically and economically possible to use district cooling. Thislimits the use to a great extent.

Another method which has been developed to manage the lack of electricalpower for the cooling machines is evaporative cooling whereby theventilation air is cooled by moisturising it with water. In moreadvanced plants both the supply and the return air is moisturised androtating heat exchangers and driers are also used. The method may inmany cases replace mechanical cooling but has its limitation in very hotclimates or in hot climates with high air humidity. Air treatment andcooling plants which are used in this cooling method are mainly inoperation only during office hours.

Another method which has been developed to manage the lack of electricalpower for the cooling machines is the use of reservoirs for storage ofchilled water coolth or ice coolth whereby the coolth is stored in wateror ice reservoirs to eliminate the power peaks during office hours, byway of a cooling machine being operating during non-office hours andcooling the reservoirs and where the stored coolth then is used tominimize the operation of the cooling machine during the hours when theelectrical transmission network system is the most loaded. A problemwith the cooling method mentioned above is that a separate storage plantis needed to buffer the cooling power which is produced. Another problemwith the cooling method mentioned above is that it is costly andcomplicated.

BRIEF DESCRIPTION OF THE INVENTION

The problem with the need of a separate storage device to buffer coolingpower is solved according to the invention by providing a method fortemporary reduction of electrical power consumption for cooling ofbuildings according to claim 1.

As the method for temporary reduction of electrical power consumptionfor cooling of buildings comprises the features in claim 1, theadvantage, that an uncomplicated and cost effective temporary reductionof electrical power consumption for cooling of a building can be carriedout, is obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference tothe accompanying drawings, where:

FIG. 1 shows schematically a module-built house in horizontal sectionthrough a story,

FIG. 2 shows schematically a slab for a module with five hollow channels(hollow cores) through which supply air can flow,

FIG. 3 shows schematically a flow chart for a part of the building,

FIG. 4 shows computer simulated cooling powers for the method accordingto the invention and the conventional method,

FIG. 5 shows how an ejector increases the cooling of the room air.

DEFINITIONS

Re-circulated room air is defined as within the building re-circulatedsupply air and return air without addition of outdoor air.

Exhaust air is defined as the air which is leaving the building throughthe exhaust air fan.

Supply air is defined as the air which is conveyed into a room. Thesupply air may, if nothing else is mentioned, consist of eitherre-circulated room air, re-circulated room air with added outdoor air oroutdoor air alone.

Cooling power is defined as the power which the cooling machine emits tothe air.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention relates to a method for temporary reduction ofelectrical power consumption for cooling of buildings where the coolingenergy is stored in slab or wall, comprising the steps of:

-   -   storing cooling energy in at least some part of the slab or the        wall by means of that, during at least one period of time when        the electrical transmission network system can supply the        necessary electrical cooling machine power, supply cooling        machine cooled supply air to channels arranged in the slab or        the wall, and    -   during at least one period of time when the electrical        transmission network system is highly loaded reduce the        electrical power consumption of the cooling machine and at the        same time convey supply air through the building through the        mentioned channels, which supply air when entering the channel        is warmer than the surrounding slab surface or wall surface        adjacent to supply air terminal devices, hereby using the        earlier in the slab or wall stored cooling energy to cool the        supply air.

In order to be able to use the invention to a maximum the ceilingsurfaces may not be covered with for example compact false ceilingswhich obstruct the absorption in the slab of the energy generated in theroom.

Conventional office buildings are provided with false ceilings which aresituated at such a large distance below the supporting slab that thespace obtained is enough to house the for each room necessary supplylines for example for electricity, heating, cooling, supply air, returnair and data, etc. Thereby the possibility for storage through theceiling area of the internal energy generated in the room is efficientlyobstructed.

The slabs may in a known manner consist of prefabricated hollow coreslabs of concrete or concrete slabs with embedded channels.

FIG. 1 shows schematically a module-built house in horizontal sectionthrough a floor, more precisely the roof slab, with a number ofunderlying rooms A, B and the corridor C. The rooms A and B are limitedby the outer walls 1, the corridor walls 2 and the room-separating walls3. Each room A consists of three modules 4 at 3×1.2 m each (see FIG. 2)where in each module three connected channels 5 are run through bysupply air from a, in the ceiling of the corridor C situated connectorterminal device 6 and supply air channel 7, which via vertical shaftsconnects to a fan room situated on the roof. The supply air from themodule 4 is then flowing through the supply air terminal device 8 intothe room A. The return air from the rooms A goes through a overflowterminal device in the corridor wall, not shown on the drawing, out tothe corridor which in this case serves as collecting channel, forfurther transport to a fan room. The floor slab in room A is used in thesame way as the roof slab for distribution of supply air. In this caseto a room situated below room A. The modules 4 are laid up on the facadewalls.

FIG. 2 shows schematically a slab for a module with five hollow channels(hollow cores) through which supply air can flow, of which according toFIG. 1 three are connected for supply air distribution.

FIG. 3 shows schematically a flow chart for a part of the building, andhow those in FIG. 1 and FIG. 2 mentioned modules 4 are connected withthe flow chart of the building. Only one module for each room isaccounted for as an example. The equipment for cooling and air-change ofthe building comprises a supply air fan 20 and a return air fan 21.Further, a heat exchanger 22, a cooling battery 23, and four motorisedcut-off valves 24, 25, 26 and 27 are included. The cooling machine 28supplies the cooling batteries with, for example cooling water, forcooling of the supply air. Via return air terminals 29 the return air inthe corridor C is transported (see FIG. 1) back to the fan room.

The plant operates in the following way: During office hours the valve26 is closed and the rotating heat exchanger 22 is in operation. Thefans 20 and 21 are turned on. The other valves are open. Outdoor aircomes in through valve 24, passes the fan 20 and is cooled through thecooling battery 23 for further transportation through the slab modules 4to the different rooms. The return air is sucked through an return airterminal device located in the corridor back to the fan room. Duringnon-office hours the fan 20 is in operation. The fan 21 and the heatexchanger 22 are turned off. The valves 26 and 27 are open. The othervalves, 24 and 25, are closed. Supply and return air now circulates inthe plant from the terminal device 29 via the valve 26 to the fan 20 andis cooled through the cooling battery 23 via modules 4 again out to therooms. This means that the room air is re-circulated in the building asno outdoor air is added.

When high electrical power capacity is available, the slabs are cooleddown. As it, during non-office hours, only is room air which isre-circulated over the cooling batteries, a low cooling power isrequired as no outdoor air is added during this time period. However,the power may be increased by lowering the supply air temperature acouple of degrees.

Alternatively, one may use a heat exchanger between the outdoor air andthe exhaust air, preferably with high efficiency, and after the heatexchange to cool down the supply air to a required temperature. Thecooling machine power and the power consumption gets higher with thismethod.

Calculation Example

Assumptions: A 10 m² office room with a facade length of 3.6 m (3×1.2 mmodule slabs) is situated at a west facade in a hot climate. The outdoortemperature is maximum 43° C., minimum 29° C. The supply air temperature+14° C. Two persons are in the room between 08-17 hours, and internalpower such as lighting, computers, printers, etc. is 25 W/m² during thesame time period. The cooling power of a plant which works according tothe invention is limited to 30% of that of a conventional mechanicalcooling plant between 11-16 hours. Similar rooms are situated above andbelow the calculated room. The calculations have been performed withEQUA's computer program; IDA Indoor Climate and Energy (ICE).

If the calculation is performed so that the room temperature in theoffice room described above of around 10 m² does not exceed 24° C. andwithout any cut-down in power, a 30 l/s larger supply air flow isrequired in the conventional case compared to the method according tothe invention. In total 70 and 40 l/s, respectively, is needed. Thereason for this is that the plant in the conventional case only is inoperation during office hours and that the larger part of the in theroom developed power must be cooled away directly as it cannot bestored.

FIG. 4 shows computer simulated cooling powers for the method accordingto the invention and the conventional method during the time period00-24.

The electrical power for the cooling machine is normally around 50% ofthe supplied cooling power.

According to the conventional method maximum 1950 W cooling power isrequired between 08-11 hours and maximum 2050 W cooling power between16-17 hours to hold the temperature requirement of 24° C. Between 11-16hours the power has been reduced to 1150 W, i.e. around 55% of themaximum power which is 2050 W. During non-office hours 17-08 hours thecooling machine is turned off.

In the conventional case the room temperature has risen at 16 hours toaround 27.5° C. Here are thus significant investments required in costlyadditional equipment, for example cooling water reservoirs, to reach theset-up savings effects.

The method according the invention needs maximum 1100 W during the timeperiod 08-11 hours and maximum 1150 W between 16-17 hours in order notto exceed the temperature requirement of 24° C. This corresponds toaround 55% of the cooling power in the conventional case. Between 11-16hours the power is reduced to 600 W, that is around 30% of the maximumpower 2050 W in the conventional case.

During non-office hours at 17-08 hours the cooling effect never exceeds500 W—which corresponds to a supply air temperature of around 14° C.—asthe room air is only re-circulated in the building and addition ofoutdoor air is not required, this because of that no or very few peopleare situated in the building during non-office hours, i.e. duringnon-working hours.

From having cooled down the slab with 14° C. supply air between 16-11hours (between 17-08 this has taken place with re-circulated room airwithout additional outdoor air) the reduced power consumption during thetime period 11-16 hours will give a supply air temperature of around 22°C. in this case. This supply air will warm up the slab from withinbetween 11-16 hours at the same time as the surface layer of the slabhas enough cooling capacity for the room air not to exceed the chosentemperature limit, in this case 24° C. Thus the slab is warmed up bothfrom within and from the outside during a limited time period.

The power requirement (power×time), in this case Kwh, corresponds withthe framed areas of the power curves. As both buildings have the sameinsulation standard, theoretically the same amount of power is requiredduring a 24 hour period, but as the invention uses the cooler night airfor cooling of the cooling machines, a better efficiency is obtainedwhich corresponds to a power saving of around 10% annually. In theconventional case the room has false ceilings.

The operative temperature (=experienced temperature=the mean value ofthe room temperature and the temperature on the surfaces which enclosethe room) is lower than the room temperature according to the invention.As the experienced temperature is lower than the actual roomtemperature, it feels cooler than what the thermometer shows. In theconvention case it is the other way around.

The reason for the large power and flow reduction according to theinvention depends on a number of co-operating elements:

The blocking time, that is when the power consumption is reduced, islimited. The five hours between 11-16 hours cannot be prolonged more inthis example without the room temperature rising to unacceptable levels,in the calculation example over 24° C. This depends on the outdoortemperature, the air humidity and the degree of density in the building,the insulation level, the re-cycling level of room air, internal powers,etc. During a shorter time period it is possible to reach larger powersavings than the 70% which have been accounted for in the examplewithout the room temperature exceeding 24° C. For example the coolingplant can be closed down completely so that the power is decreased tozero (0) during two hours.

The slab as power storage must have enough capacity (mass) and be ableto transport necessary air in the hollow channels. The slab surfaces,that is the roof and floor surfaces, must be accessible, that is thickcarpets, false ceilings, sound absorbing baffles, etc. must be installedin a way so that the heat transfer by convection or by radiation is nothindered to any greater extent.

The largest part of the energy developed in the room shall during theactual time 11-16 hours be transferred to the slab in order to duringthe other hours of the day be transported away with cooled supply airwhich during non-office hours consists of re-circulated room air.

There are a number of alternative embodiments of the now describedmethod within the scope of the inventive idea to further reduce thecooling power.

A conceivable possibility is to reduce the supply air flow during ashorter time period when the electrical transmission network system ishighly loaded. The air flow shall always be arranged so that odour frompeople, building materials, moisture, etc. does not become troublesome.This corresponds to a minimum air flow of around 6-10 l/s and person. Inrooms with high internal heat development and/or very hot outdoorclimate, the mentioned supply air flows are not enough, when air coolingof rooms, in order to meet the comfort requirements. As appears from theexample above, according to the invention, 40 l/s and in theconventional case 70 l/s, is required to obtain a good indoor climate.If 8 l/s and person is chosen in the calculated case according to theinvention, this corresponds to 16/40=0.4 times the original flow, thatis 0.6 times lower flow during a shorter time period, corresponding to60% lower cooling power during the same time period. The methodaccording to the invention has, according to FIG. 4, reduced the powerto 30%. If during one hour the flow and/or the power together arereduced with an additional 60%, the total power use will now be 0.40times 30%=12% of the original 2050 W. The assumption here is that asmall increase of the room temperature can be accepted, in this case0.5-1° C.

Another conceivable possibility to reduce the cooling machine power isthat, as is shown in FIG. 4, to introduce in the flooring channels 41 anejector 42, or a fan with low power, which through the driving forcecreated by the supply air or the fan together with it sucks room air 43which is cooled down in the slab and after having passed the supply airterminal device 44 contributes to the cooling of the room.

In the described embodiment slabs have been used for storage of coolingenergy. However, it is also possible that also, or alternatively, storecooling energy in walls such as inner and/or outer walls in buildings ina similar way.

1. Method for temporary reduction of electrical power consumption forcooling of buildings where the cooling energy is stored in slab or wall,comprising the step of: storing cooling energy in at least some part ofthe slab or the wall by means of that, during at least one period oftime when the electrical transmission network system can supply thenecessary electrical cooling machine power, supply cooling machinecooled supply air to channels arranged in the slab or the wall, andfurther characterized by the step, that: during at least one period oftime when the electrical transmission network system is highly loaded,reduce the electrical power consumption of the cooling machine and atthe same time convey supply air through the building through thementioned channels, which supply air when entering the channel is warmerthan the surrounding slab surface or wall surface adjacent to supply airterminal devices, hereby using the earlier in the slab or wall storedcooling energy to cool the supply air.
 2. Method according to claim 1,characterized by the step, that the slab or wall is made of concrete. 3.Method according to claim 1, characterized by the step, to store coolingenergy in slabs of prefabricated hollow core slabs or cast-in-situconcrete slabs with embedded channels.
 4. Method according to claim 1,characterized by the step, to store cooling energy in at least some partof the slab or the wall by, during at least one period of time whenaddition of outdoor air is not required, re-circulating cooling machinecooled room air in channels arranged in the slab or the wall.
 5. Methodaccording to claim 1, characterized by the step, to reduce theelectrical power consumption for the cooling machine by decreasing thesupply air flow during at least a period of time when the when theelectrical transmission network system is highly loaded.
 6. Methodaccording to claim 1, characterized by the step, that with theassistance of an ejector, or a fan, further cool the room air by thatparts of the room air is passed through the slab or the wall.